Mobile contactless application based on a mobile communication device is currently an active application field on both technology and market, among which Near Field Communication (NFC) technology is a typical representative. NFC technology has developed for several generations, and relative technical standards and application specifications (such as ISO18092 or ISO21481) are becoming more and more mature. However, relative products land on the market much more slowly than expectation. The reasons for the slow entry include complicated application and business models caused by a long industrial chain in NFC technology. Additionally, Single Wire Protocol (SWP) used in the conventional solutions has a bad compatibility with technologies in existing contactless application systems, which becomes a main obstacle in technical level. Technical details about SWP have been described in Chinese patent publication No. CN 101103582A.
Electronic payment service has gone deep into our life and brought us much convenience. In fixed business sites, electronic payment service based on Proximity Integrated Circuit Card (PICC) has developed mature solutions and stable markets. Along with the development of applications, it is desired that PICC is applied in mobile communication devices. For example, it is expected to have display functions to inquire data inside PICC and to have communication functions for communicating with a backend server to realize some functions like remote recharging of an electronic wallet. In other words, a cell phone is expected to be a kind of PICC. Therefore, a new product combining a PICC, a Proximity Coupling Device (PCD) and a cell phone terminal together based on NFC appeared in 2004.
As a result of technological development and standardization, technical standards and application specifications relative to NFC are more mature than ever. However, products based on NFC have not landed on the market yet. One major limitation lies in that characteristics of a PICC can not be reflected completely, although a NFC device has realized an emulation of a PICC in function. Especially, the requirement that the NFC device should be compatible with characteristics of the PICC used in legacy application systems causes a stricter condition to land on the market for some tremendously influential contactless applications already in use. For example, public transportation systems and micropayment systems need to modify installed equipment, such as Point-Of-Sale (POS) machine, which thereby bring about high change costs and business costs. Therefore, terminal device manufacturers are not motivated to provide cell phone terminals supporting NFC, brand new designed products, because of a lack of a mature application environment, which thereby slows progresses of practical application popularization of NFC.
In substance, NFC is an application of PICC, with a carrier of a PICC changed. From the view of structures, NFC is realized by employing a dual element architecture, e.g., a combination of a ContactLess Front (CLF) element and a Security Element (SE) as shown in FIG. 1. The contactless front element is configured to process a contactless Radio Frequency (RF) interface and a communication protocol. The security element is configured to process applications and data management of PICC. Advantages of the architecture are as follows.
1) Separated card and station may be realized easily by employing a dual element architecture of contactless front element and security element. The contactless front element is integrated in a NFC terminal to realize a complete contactless RF interface. PICC applications deal with many security requirements. Before entering an application step, a PICC needs to be issued and managed. The security element, separated from the NFC terminal, can be independently issued and is easily compatible with existing systems in management.
2) The PICC is always a closed application environment. A same type of PICC in different regions or different applications may have different initial configuration. Under an architecture of contactless front element and security element, a general NFC terminal can be arranged with different security element to realize different application demands.
3) The contactless front element and its RF antennas are integrated on the NFC terminal, thereby facilitating a consistent contactless RF interface.
The NFC terminal realizes an emulation of a PICC through a combination of the contactless front element and the security element, where a connection interface needs to be defined between the contactless front element and the security element. As shown in FIG. 2, for a NFC terminal scheme, the security element is generally realized by a SIM (Subscriber Identity Module) card and an interface therein is a Single Wire Protocol (SWP) interface. A SIM card security element supporting a SWP interface is called SWP SIM, which communicates with the contactless front element through the C6 pin of the SIM card to realize a NFC function.
The NFC standard ISO18092, supporting the emulation of a PICC, is built on the standard ISO14443. Since the SWP interface has defined a complete set of communication protocols, when ISO14443 protocol data packets are transmitted between the security element and the contactless front element, the ISO14443 data packets need to be converted into packets satisfying the SWP protocol, and a Logical Link Control (LLC) layer and a Medium Access Control (MAC) layer need to be added. The converted data packets, the LLC layer and the MAC layer form a SWP data frame, as shown in FIG. 3.
When frame data following ISO18092 or ISO14443 is converted into Contactless Tunnelling (CLT) frames, five bytes are added, including Start-Of-Frame (SOF), LLC control field, Cyclic Redundancy Check (CRC) 16 and End-Of-Frame (EOF). Under a speed of SWP 848 Kbps, the smallest delay of an ideal reception and sending is still more than 113 μs. The more the application data is, the more the delay is.
A contactless application layer protocol defined by ISO14443-4 has no strict requirement on response time. Therefore, the SWP interface can realize an emulation of a PICC while the overtime of a proximity coupling device waiting for responses should be set relatively longer to avoid a problem of compatibility, which is a first problem that the SWP interface needs to face.
According to requirement of ISO14443-3, the command sets of request, wake-up, anticollision, and select have been defined that the minimum response time of a PICC to a proximity coupling device is 1172/Fc (Fc being an external field clock frequency, 13.56 MHz), namely, 86 μs in time. Even if using a standard limit speed of the SWP interface in addition to data processing time in elements, the time required is far greater than 86 μs. Therefore, these commands can not be realized through the SWP interface in time. In existing NFC solutions, commands of ISO14443-3 are responded directly by the contactless front element; when it comes to ISO14443-4 protocol, the proximity coupling device is responded by the security element through the SWP interface.
An emulation of a PICC realized in this manner is similar to a general PICC in function except for a little increment of delay. However, there is a relatively serious problems underlying. Commands defined in ISO14443-3 may process UID of a PICC. In many legacy systems, UID is a very important factor to be used to disperse the key, which realize the one-card-one-key management. When protocol ISO14443-3 is completed by the contactless front element, it is the contactless front element that informs the UID to the proximity coupling device. Therefore, when the SWP SIM card is put into the NFC terminal, the UID of the SWP SIM card needs to be transmitted to the contactless front element and saved therein through a synchronous operation. UID of a common Integrated Circuit (IC) card is not allowed to be modified after leaving the factory, and IC manufacturers and operating agencies have drafted various regulations to ensure the uniqueness of UID. Due to an architecture of separated card and station, different SWP SIM cards may be put into a same NFC terminal, which means that UID of the contactless front element should be modifiable. Once the UID is modified, UID's uniqueness management will face a major challenge, which will lead to confusing account management of some application systems, lower security of the system, such as lowering the difficulty in cloning the card.
In conclusion, although SWP SIM has become a main solution in NFC communication and corresponding technical standards have also been drafted, problems of delay in a SWP interface and a UID management deriving therefrom may have some influences on further development of NFC. Therefore, a more effective solution is desired.